PMC-Sierra PM5349 manual Descramble, Error Monitor, Loss of Signal

PMC-Sierra, Inc.

S/UNI-QUAD

DATASHEET

PM5349 S/UNI-QUAD

PMC-971239 ISSUE 6 SATURN USER NETWORK INTERFACE (155-QUAD)

While in-frame, the framing bytes (A1, A2) in each frame are compared against the expected pattern. Out-of-frame is declared when four consecutive frames containing one or more framing pattern errors have been received.

While out-of-frame, the SIPO block monitors the receive stream for an occurrence of the framing pattern. When a framing pattern is recognized, the Framer block verifies that an error free framing pattern is present in the next frame before declaring in-frame.

10.2.2Descramble

The Descramble Block utilizes a frame synchronous descrambler to process the receive stream. The generating polynomial is x7 + x6 + 1 and the sequence length is 127. Details of the de-scrambling operation are provided in the references. Note that the framing bytes (A1 and A2) and the trace/growth bytes (J0/Z0) are not descrambled. A register bit is provided to disable the de- scrambling operation.

10.2.3Error Monitor

The Error Monitor Block calculates the received section BIP-8 error detection code (B1) based on the scrambled data of the complete STS-3c (STM-1) frame. The section BIP-8 code is based on a bit interleaved parity calculation using even parity. Details are provided in the references. The calculated BIP-8 code is compared with the BIP-8 code extracted from the B1 byte of the following frame. Differences indicate that a section level bit error has occurred. Up to 64000 (8 x 8000) bit errors can be detected per second. The Error Monitor Block accumulates these section level bit errors in a 16-bit saturating counter that can be read via the microprocessor interface. Circuitry is provided to latch this counter so that its value can be read while simultaneously resetting the internal counter to 0 or 1, if appropriate, so that a new period of accumulation can begin without loss of any events. It is intended that this counter be polled at least once per second so as not to miss bit error events.

10.2.4Loss of Signal

The Loss of Signal Block monitors the scrambled data of the receive stream for the absence of 1's. When 20 ± 3 µs of all zeros patterns is detected, a loss of signal (LOS) is declared. Loss of signal is cleared when two valid framing words are detected and during the intervening time, no loss of signal condition is detected. The LOS signal is optionally reported on the RALRM output pin when enabled by the LOSEN Receive Alarm Control Register bit.

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